The present invention relates to a film sag detecting device for a sound cinecamera.
Referring to FIG. 1 showing a typical film sag detecting device in accordance with the prior art, the sound cinecamera is provided with a motor 2 and a film advancing tool 3 for intermittent feeding of a film for exposure, a motor 5, a capstan 6 and a pinch roller 7 for continuous feeding of the film for recording sounds on it by means of a sound recording head 4 and a film sag detecting device including a detecting lever 8. The aforementioned means, in combination, performs a function of maintaining the film sag at an appropriate amount in the film path formed between the film advancing tool 3 and the capstan 6 so as to achieve the desired smooth junctioning of both the film advancing tool 3 and the capstan 6.
The aforementioned film sag detecting device in accordance with the prior art consists of the detecting lever 8 attached with a film sag detecting element on one end thereof and also rotatably supported by a supporting pin 10, a tension spring 9 applied to detecting lever 8, an arm branching from the detecting lever 8 and forming a blind 11 on one end thereof, and a light emitting diode 12 and a photo transistor 13 respectively placed on either side of the blind 11 within the operation area thereof.
Supposing an excessive sag occurs in the film path between the film advancing tool 3 and the capstan 6, the excessively sagging film 1 pushes the detecting lever 8 down to cause a clockwise rotation of said lever around the pin 10 against the tension spring 9. This action moves the arm branching from the detecting lever 8 to cause the blind 11 formed on one end thereof to interrupt the light path bridging the light emitting diode 12 and the photo transistor 13. As a result, the light beam received by the photo transistor 13 is interrupted to cause the electric circuits including the photo transistor 13 and the motor 2 to reduce the film feeding rate of the film advancing tool 3, thereby correcting the excessive sag of the film 1.
As mentioned above, the utilization of the photoelectric means is rather limited, and the film sag detecting device of the prior art predominantly relies on mechanical means, such as the detecting lever 8 for direct detection of excessive film sag. This causes various faults including a considerable possibility of frequent occurrence of mechanical failure and the inherent requirement for a rather large space in the camera body. Another fault to be recognized in the prior art is the inconvenience incurred when loading a camera with a film cartridge caused by the necessity to keep pushing the detecting lever 8 downwardly during the film loading operation, because the customary setup of a camera requires that it be loaded with a film cartridge from the front or downward from the front side to the back side of the page in FIG. 1.